Fuel system with vapor bypass of oil-fuel mixer halting oil pumping

ABSTRACT

A marine propulsion system (200) having an outboard two cycle internal combustion engine (212) and an oil-fuel mixing fuel delivery system (2, 5, 7) has a vapor separator (702) connected to prevent excess oil in the mixture as fuel runs out. The vapor separator (702) has a fuel inlet (704) receiving fuel from the fuel tank (5), a fuel outlet (706) delivering fuel to the fuel inlet (4) of the oil-fuel mixer (2), and a vapor outlet (708) delivering vapor or air through a bypass connection (710) to the suction intake side of a fuel pump (11) and bypassing the mixer (2). The fuel pump (11) suctions oil-fuel mixture from the mixer (2). When the fuel tank (5) runs out of fuel, then air from the fuel tank (5) is sucked through the bypass connection (710) rather than through the mixer (2), which termination of flow through the mixer (2) stops further delivery of oil from the oil tank (7) to the engine (212) which would otherwise cause an overly rich oil-fuel mixture supplied to the engine (212) from the remaining oil-fuel mixture in a carburetor bowl or the like. The invention also maintains accuracy of the oil-fuel mixture ratio during normal operation.

BACKGROUND AND SUMMARY

The present invention relates to marine propulsion systems having anoutboard two cycle internal combustion engine and a remote fuel tank,and more particularly to the fuel delivery system therefore.

The invention arose during development efforts directed toward solving aproblem occuring as fuel runs out in systems using an automatic oil-fuelmixer, sometimes referred to as an autoblend unit, for example as shownin U.S. Pat. No. 4,583,500, incorporated herein by reference. The mixerdraws fuel from a fuel tank and oil from an oil tank in a given ratio,typically about 50 parts fuel to 1 part oil, and automatically mixes thefuel and oil, eliminating the need to premix same. The mixer has a fuelinlet, an oil inlet, and an oil-fuel outlet, and is operated by apressure differential between the fuel inlet and the oil-fuel outlet.The mixer may be operated by various sources of pressure differential,for example the mixer may be connected downstream of the fuel pump anduse fuel pressure to operate the mixer. In other applications where apressurized fuel tank is utilized, such pressure may be used to operatethe mixer. In other implementations, crankcase pressure and/or vacuummay be used to operate the mixer, or a separate dedicated small pump maybe used. In another implementation, the mixer is connected upstream ofthe fuel pump such that fuel pump suction on the oil-fuel outletoperates the mixer. In all the implementations, a problem of an overlyrich oil-fuel mixture being supplied to the engine arises as fuel runsout.

In the last noted implementation, when the fuel tank runs out of fuel,then air from the tank is sucked through the mixer by the fuel pump.This air flow through the mixer continues to operate the mixer andcauses continued delivery of oil from the oil tank to the engine, whichin turn causes excess oil in the oil-fuel mixture as the fuel runs out,i.e. there is an overly rich oil-fuel mixture supplied to the enginefrom the remaining oil-fuel mixture in a carburetor bowl or the like asthe latter runs dry.

The present invention addresses and solves the noted problem. Anothersolution is shown in copending application Ser. No. 07/218,310, filed oneven date herewith, entitled "Automatic Oil-Fuel Mixer With AuxiliaryChamber".

It has also been found that the present invention enhances accuracy ofthe oil-fuel mixture ratio. In order to provide an accurate mix, thefuel must be in liquid form. If the fuel is in the form of vapor or ifthere are vapor or air bubbles in the fuel, then such air or vapor willdisplace the fuel in the mixer, and the oil-fuel mixture ratio will notbe accurate. In the worst case, when only air is being drawn through themixer as above noted when fuel runs out, then the mixer will provide alloil and no fuel. The present invention ensures that only fuel in theliquid form is mixed with the oil in the mixer, to maintain accuracy ofthe mixture ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a marine propulsion system and fuel deliverysystem known in the prior art.

FIG. 2 shows a marine propulsion system and fuel delivery system inaccordance with the invention.

DETAILED DESCRIPTION

FIGS. 1 and 2 use like reference numerals from incorporated U.S. Pat.No. 4,583,500 where appropriate to facilitate clarity. FIG. 1 shows amarine propulsion system 200 including an outboard propulsion unithaving a powerhead 201 with a two cycle crankcase compression internalcombustion engine 212 and having a lower depending gearcase 203 andpropeller 204, and mounted to the transom of a boat (not shown) bytransom bracket 205. A remote fuel tank 5 is within the boat. Anoil-fuel mixer 2, as shown in incorporated U.S. Pat. No. 4,583,500,draws fuel from fuel tank 5 and oil from oil tank 7, and delivers anoil-fuel mixture to the engine. Mixer 2 has a fuel inlet 4 receivingfuel from fuel tank 5, an oil inlet 6, 8 receiving oil from oil tank 7,and an oil-fuel outlet 10 at port 20, FIGS. 2-4 of U.S. Pat. No.4,583,500, delivering the oil-fuel mixture to the intake suction vacuumside of fuel pump 11, which is a crankcase pressure pulse driven pump,Mercury Marine Brunswick Corp. Outboard Service Training Notebook,Bulletin 90-90592 3-1286, pages 10-11, and for example U.S. Pat. No.3,924,975, incorporated herein by reference. Mixer 2 is operated by apressure differential between fuel inlet 4 and oil-fuel outlet 10. Fuelpump 11 suctions the oil-fuel mixture from oil-fuel outlet 10 of themixer to provide such pressure differential.

As above noted, a problem with excess oil in the mixture occurs whenfuel tank 5 runs out of fuel, because air from fuel tank 5 is thensucked through mixer 2 to operate same, such that the mixer continues topump oil from oil tank 7 to oil-fuel outlet 10, whereby the mixturecontains all oil and no fuel. This in turn causes an overly richoil-fuel mixture to be supplied to the engine from the remaining mixturein a carburetor bowl, fuel injection system, or the like as the latterruns dry.

The present invention is shown in FIG. 2, and like reference numeralsare used from FIG. 1 where appropriate to facilitate clarity. A vaporseparator 702 is connected between fuel tank 5 and mixer 2. The vaporseparator has a fuel inlet 704 receiving fuel from fuel tank 5, a fueloutlet 706 delivering vapor-free fuel to mixer 2, and a vapor outlet 708delivering fuel vapor or air through bypass connection 710 to theengine, such that the vapor bypasses mixer 2. A float actuated shut-offvalve 712 in the vapor separator closes outlet 708 when the fuel levelin the vapor separator rises to a given level. The valve has a float 714connected by lever 716 to pivot point 718 fixed to the vapor separator,such that as the fuel level in vapor separator 702 rises, valve member720 moves upwardly to close outlet 708. When sufficient vapor or air ispresent, the fuel level lowers and valve 712 opens and allows the vaporor air to flow directly to outlet 10 of the mixer. When no vapor or air,or only a minimum amount thereof, is present, valve 712 closes. Vaporfrom outlet 708 is delivered through bypass connection 710 to thesuction intake side of fuel pump 11 at oil-fuel outlet 10 of mixer 2.

When fuel tank 5 runs out of fuel, the fuel level in vapor separator 702lowers, whereby valve 712 opens. Hence, air from tank 5 is suckedthrough open vapor outlet 708 and bypass connection 710, rather thanthrough mixer 2. This termination of flow through mixer 2 stopsoperation thereof, whereby to stop pumping of oil thereby and hence stopfurther delivery of oil from oil tank 7 to the engine.

Another benefit of the invention is that during normal running of theengine, if there is vapor in the fuel, such vapor will rise in vaporseparator 702 such that the fuel level in the latter lowers, which inturn opens valve 712 and allows escape of such vapor through bypassconnection 710, bypassing mixer 2. This maintains accuracy of themixture ratio by preventing substitution of vapor or air for liquid fuelin mixer 2, which would otherwise alter the mixture ratio.

It is recognized that various equivalents, alternatives andmodifications are possible within the scope of the appended claim.

I claim:
 1. A marine propulsion system comprising an outboard two cycleinternal combustion engine, a fuel tank, an oil tank, an oil-fuel mixerhaving a fuel inlet receiving fuel from said fuel tank, an oil inletreceiving oil from said oil tank, and an oil-fuel outlet delivering anoil-fuel mixture to said engine, a vapor separator coupled to said mixerand removing fuel vapor from said fuel, wherein said vapor separator isconnected between said fuel tank and said mixer.
 2. The inventionaccording to claim 1 wherein said vapor separator has a fuel inletreceiving fuel from said fuel tank, and a fuel outlet deliveringvapor-free fuel to said mixer.
 3. The invention according to claim 2wherein said vapor separator has a vapor outlet delivering vapor to saidengine, such that said vapor bypasses said mixer.
 4. The inventionaccording to claim 1 wherein said vapor separator has a vapor outlet,and comprising in combination a float actuated shut-off valve in saidvapor separator responsive to a given fuel level in said vapor separatorto close said vapor outlet of said vapor separator.
 5. A marinepropulsion system comprising an outboard two cycle internal combustionengine running on an oil-fuel mixture, a fuel system preventing excessoil in said mixture as said fuel runs out, comprising a fuel tank, anoil tank, an oil-fuel mixer having a fuel inlet receiving fuel from saidfuel tank, an oil inlet receiving oil from said oil tank, and anoil-fuel outlet delivering an oil-fuel mixture to said engine, saidmixer being operated by a pressure differential between said fuel inletand said oil-fuel outlet, a fuel pump suctioning said oil-fuel mixturefrom said oil-fuel outlet of said mixer to provide said pressuredifferential, and pumping said oil-fuel mixture to said engine, a vaporseparator connected between said fuel tank and said mixer, said vaporseparator having a fuel inlet receiving fuel from said fuel tank, a fueloutlet delivering fuel to said fuel inlet of said mixer, and a vaporoutlet delivering vapor through a bypass connection to said fuel pumpand bypassing said mixer, such that if said fuel tank runs out of fuel,then air from said tank is sucked through said bypass connection ratherthan through said mixer, to terminate the flow through said mixer andstop operation of said mixer and stop further delivery of oil from saidoil tank to said engine which would otherwise cause an overly richoil-fuel mixture supplied to said engine from the remaining oil-fuelmixture in a carburetor bowl or the like.
 6. The invention according toclaim 5 wherein said vapor separator has a float actuated shut-off valveresponsive to a given fuel level in said vapor separator to close saidvapor outlet of said vapor separator.